<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
      body>div{
        width: 200px;
        /*height: 200px;*/
        border: 1px solid red;
        /*当元素的所有子元素全部浮动时,自动识别的高度为0,此时后面的元素会顶上来导致
        元素层叠的显示异常,给元素添加overflow:hidden解决此问题*/
        overflow: hidden;

      }
      div>div{
        width: 50px;
        height: 50px;
      }
      #d1{
        background-color: red;
        float: right;
      }
      #d2{
        background-color: green;
        float: right;
      }
      #d3{
        background-color: blue;
        float: left;
      }

      ul{
        list-style-type: none;/*去掉图标*/
        margin: 0;
        padding: 0;
        overflow: hidden;
      }
      ul>li{
        float: left;
        padding-right: 20px;

      }
      a{
        text-decoration: none;
        color: black;
      }

    </style>
</head>
<body>
<ul>
  <li><a href="">首页</a></li>
  <li><a href="">免费课</a></li>
  <li><a href="">直播课</a></li>
  <li><a href="">精品课</a></li>
  <li><a href="">线上班</a></li>
</ul>

<div>
  <div id="d1"></div>
  <div id="d2"></div>
  <div id="d3"></div>

</div>
</body>
</html>